The International Association of Machinists released internal documents from Boeing that it says bolsters the claim from the National Labor Relations Board that the company moved production to South Carolina because of labor issues. The documents say that officials felt the South Carolina location would restore balance to their labor relationship, though they also said that the costs would be much more than adding capacity to current plants, and that the South Carolina plant was more likely to fail. Boeing says that the documents do not prove anything, and that the reasons for their decision do not break the law. The NLRB filed a complaint against Boring in June, and hearings are ongoing.
See "Boeing Union Presses Plant Relocation Issue", David Kesmodel and Melanie Trottman, The Wall Street Journal, September 25, 2011